1. Field of Technology
The present invention relates generally to antennas, and more specifically to multiple frequency band antennas that are particularly suited for use in wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication devices.
2. Description of the Related Art
Different types of wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication apparatus are available. Many of these devices are intended to be easily carried on the person of a user, often fitting in a shirt or coat pocket.
The antenna assembly configuration of a mobile communication device can significantly affect the overall size or footprint of the device. For example, cellular telephones typically have antenna assembly structures that support communication in multiple operating frequency bands, such as GSM 800 MHz/900 MHz/1800 MHz/1900 MHz bands, UMTS 2100 MHz band, and communication in the 5 GHz band. In addition the mobile communication device often is capable of interfacing with peripheral equipment using the 2450 MHz band and wireless technology such as Bluetooth® (registered trademark of Bluetooth Sig, Inc., Bellevue, Wash., USA). Various types of antenna for mobile devices are used, such as helical, “inverted F”, folded dipole, and retractable antenna assembly structures, for example. Helical and retractable antenna are typically installed outside a mobile device, and inverted F antenna are usually located inside of a case or housing of a device. Generally, internal antenna are used instead external antenna for mobile communication devices for mechanical and ergonomic reasons. Internal antenna are protected by the case or housing of the mobile device and therefore tend to be more durable than external antenna. External antenna also may physically interfere with the surroundings of a mobile device and make a mobile device difficult to use, particularly in limited-space environments.
In some types of mobile communication devices, however, known internal structures and design techniques provide relatively poor communication signal radiation and reception, at least in certain operating positions. One of the biggest challenges for mobile device design is to ensure that the antenna assembly operates effectively for various applications, which determines antenna assembly position related to human body. Typical operating positions of a mobile device include, for example, a data input position, in which the mobile device is held in one or both hands, such as when a user is entering a telephone number or email message; a voice communication position, in which the mobile device may be held next to a user's head and a speaker and microphone are used to carry on a conversation; and a “set down” position, in which the mobile device is not in use by the user and is set down on a surface, placed in a holder, or held in or on some other storage apparatus. In these positions, parts of a users body and other ambient objects can block the antenna assembly and degrade its performance. Known internal antennas, that are embedded in the device housing, tend to perform relatively poorly, particularly when a mobile device is in a voice communication position. Although the mobile device is not actively being employed by the user when in the set down position, the antenna assembly should still be functional at least receive communication signals.
The desire to maintain the configuration of the mobile communication device to a size that conveniently fits into a hand of the user, presents a challenge to antenna assembly design. This presents a tradeoff between the antenna assembly performance, which dictates a relatively larger size, and the available space for the antenna assembly within the device. Larger internal antenna assembly assemblies often directly affect the thickness of the mobile communication device.
Therefore, it is desirable to reduce the thickness of the antenna assembly so that the mobile communication device can be made as slim as possible.